1. Field of the Invention
The present invention relates to an alternator driven by an internal combustion engine for a passenger car, a truck or a boat.
2. Description of the Related Art
Recently, installation of various safety control systems have necessitated an increase in the output power of an alternator. On the other hand, as engine noises have been reduced to comply with the social demand for noise reduction in vehicles, noises of an engine accessories such as an alternator has come into question.
Noises of the alternator are mainly caused by cooling air blowing on uneven coil-end groups or portions of the stator winding.
JP-A-59-159638 discloses an alternator which has a rotor with cooling fans and a stator with a multi-phase stator winding wound by a continuous wire. The stator winding has flattened coil-end groups to increase the surface area to be cooled by the flow of the cooling air.
However, coil-end groups of the multi-phase stator winding wound by a continuous wire are necessarily formed unevenly because each phase winding interferes with each other in the circumference thereof. Thus, cooling air blows on the uneven inside structure, thereby generating noises.
WO92/06527 discloses an alternator in which U-shaped conductors having a U-turn portion are inserted into respective slots of a stator core from a certain direction. Each of the ends opposite the U-turn portion of the U-shaped conductors are, thereafter, connected to form a stator winding. Thus, the stator winding has a coil-end group including the U-turn portions and a coil-end group including the joint portions. The U-shaped conductors are disposed even in the slots, and the space factor of the conductors in the slot becomes high and the output power can be increased.
While the coil-end group having the U-turn portions conductors form even air-passages, the coil end groups having joint portions form walls on which cooling air blows on to increase noise. However, no specific cooling structure to reduce noises is shown therein.